A method of directly drawing on a printing plate material with laser light based on the image data by a computer is studied for printing newspaper and the like. In particular, since semiconductor laser and solid laser having output power at infrared area have characteristics in stability, cost, output power and compactness, the development of a photosensitive resin composition having photosensitive properties at a wavelength area suitable for such laser (in particular, a negative-type photosensitive resin composition in which an irradiated portion is cured) has been desired.
Such photosensitive resin composition used for negative-type printing plate material contains generally an alkali soluble resin, an infrared absorbing dye, a polymerization initiator and a compound containing an ethylenically unsaturated double bond. When light is irradiated, the composition forms a cured portion by polymerization of the compound having an ethylenically unsaturated double bond. The portion where light is not irradiated is removed by development based on its alkali soluble nature. Performances such as durability and adherence are generally required for the composition. In order to introduce the durability, it is considered to introduce double bonds to the side chains of alkali soluble resins (see JP-A-2000-187322).